Physical parameters of red supergiants in dwarf irregular galaxies in the Local Group

¹ Instituto de Astrofísica de Canarias, Avenida Vía Láctea, 38205 La Laguna, Tenerife, Spain
e-mail: britavskiy@iac.es
² Universidad de La Laguna, Dpto. Astrofísica, 38206 La Laguna, Tenerife, Spain
³ IAASARS, National Observatory of Athens, 15236 Penteli, Greece
⁴ Centro de Astrobiología (CSIC/INTA), 28850 Torrejón de Ardoz, Madrid, Spain
⁵ Grantecan S. A., Centro de Astrofísica de La Palma, Cuesta de San José, 38712 Breña Baja, La Palma, Spain
⁶ Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218, USA
⁷ European Southern Observatory, Alonso de Córdova 3107, Casilla 19001, Santiago de Chile, Chile
⁸ Rutgers University, Department of Physics and Astronomy, 136 Frelinghuysen Road, Piscataway, NJ 08854, USA

Received: 5 February 2019
Accepted: 24 September 2019

Abstract

Context. Increasing the statistics of evolved massive stars in the Local Group enables investigating their evolution at different metallicities. During the late stages of stellar evolution, the physics of some phenomena, such as episodic and systematic mass loss, are not well constrained. For example, the physical properties of red supergiants (RSGs) in different metallicity regimes remain poorly understood. Thus, we initiated a systematic study of RSGs in dwarf irregular galaxies (dIrrs) in the Local Group.

Aims. We aim to derive the fundamental physical parameters of RSGs and characterize the RSG population in nearby dIrrs.

Methods. The target selection is based on 3.6 μm and 4.5 μm photometry from archival Spitzer Space Telescope images of nearby galaxies. We selected 46 targets in the dIrrs IC 10, IC 1613, Sextans B, and the Wolf-Lundmark-Melotte (WLM) galaxy that we observed with the GTC–OSIRIS and VLT–FORS2 instruments. We used several photometric techniques together with a spectral energy distribution analysis to derive the luminosities and effective temperatures of known and newly discovered RSGs.

Results. We identified and spectroscopically confirmed 4 new RSGs, 5 previously known RSGs, and 5 massive asymptotic giant branch (AGB) stars. We added known objects from previous observations. In total, we present spectral classification and fundamental physical parameters of 25 late-type massive stars in the following dIrrs: Sextans A, Sextans B, IC 10, IC 1613, Pegasus, Phoenix, and WLM. This includes 17 RSGs and 8 AGB stars that have been identified here and previously.

Conclusions. Based on our observational results and PARSEC evolutionary models, we draw the following conclusions: (i) a trend to higher minimum effective temperatures at lower metallicities and (ii) the maximum luminosity of RSGs appears to be constant at log(L/L_⊙)≈5.5, independent of the metallicity of the host environment (up to [Fe/H] ≈ −1 dex).